Limosilactobacillus fermentum LF61: A multidimensional study on safety and functionality from genomics to clinical application.

Genomic analysis of LF61 revealed no virulence factors, drug resistance genes, or toxin synthesis gene clusters in its chromosome or plasmid.

• The chromosome size was 2.04 Mb and the plasmid size was 15.5 kb.
• No virulence factors were detected using the VFDB database.
• No drug resistance genes were detected using the CARD database.
• No toxin synthesis gene clusters were detected using antiSMASH.
• The strain met EFSA's QPS (Qualified Presumption of Safety) safety criteria.

LF61 demonstrated high survival rates under simulated gastrointestinal conditions in vitro.

• Survival rate was greater than 98% after 2-hour exposure to gastric acid at pH 2.0.
• Survival rate was 99.66% in intestinal fluid at pH 8.0.

LF61 was nontoxic to Caco-2 cells at tested concentrations.

• Metabolic activity of Caco-2 cells at 20% LF61 concentration was 100.3 ± 2.1%, indicating no cytotoxicity.
• This assessment was conducted as part of in vitro safety testing.

Acute oral toxicity testing in ICR mice demonstrated that LF61 has an LD50 greater than 2 × 10^10 CFU/kg.

• The study used ICR mice as the animal model.
• No lethal dose was established at the highest tested dose, placing LD50 above 2 × 10^10 CFU/kg.
• This result supports classification of LF61 as having low acute oral toxicity.

In a randomized, double-blind clinical trial, daily intake of LF61 for 8 weeks significantly increased serum levels of the antimicrobial peptide LL-37.

• The clinical trial included n = 49 participants.
• The dose administered was 3 × 10^10 CFU of LF61 daily for 8 weeks.
• Serum LL-37 levels increased by 12.3% (p < 0.05).

Daily LF61 supplementation for 8 weeks significantly increased serum immunoglobulin levels IgA, IgG, and IgM.

• IgA increased by 18.7% (p < 0.05).
• IgG increased by 15.2% (p < 0.05).
• IgM increased by 9.8% (p < 0.05).
• These changes were observed in the randomized double-blind trial with n = 49 participants receiving 3 × 10^10 CFU daily.

Metagenomic analysis showed that LF61 supplementation promoted colonization by short-chain fatty acid-producing bacteria.

• Bacteria promoted included Mitsuokella and Turicibacter, both with linear discriminant analysis (LDA) scores greater than 3.
• LF61 activated the carbohydrate metabolism pathway (p = 0.002).
• Alpha-diversity of the gut microbiome remained stable, as indicated by a Shannon index with p > 0.05, suggesting LF61 did not disrupt overall microbial diversity.

LF61 was isolated from human milk, which informed its selection as a candidate probiotic strain.

• The strain's origin from human milk was noted as part of its characterization.
• Human milk is considered a source of potentially safe and human-adapted probiotic strains.